As other pointed out that is payroll tax, not income tax. The differences in tax between the US and Australia are not so much in the headline rates as in the d

As other pointed out that is payroll tax, not income tax. The differences in tax between the US and Australia are not so much in the headline rates as in the deductions. In the US mortgage interest on a home you live in is tax deductible. And in the US you get taxed as an economic unit with your spouse and children. So a home owner with a big mortgage and a spouse at home looking after kids pays much less tax in the US.